In some of the most recent cases, the manhole covers had either been left completely unattached, or were improperly fitted allowing leakage into the adjacent cargo hold when the tank was filled.
The Club notes that manhole covers on vertical bulkheads, such as those on wing tanks or side tanks of container ships, are generally located close to the bottom of the tank meaning that leakage from the cover is found only after the tank has been filled to a certain head. This makes it even more difficult for the manhole cover to be secured until the contents of the tank have been transferred from the tank to stop the leakage.
The extent of damage caused in such a case will often depend on how quickly the leakage is identified and the scope for quickly transferring out the contents. Side tanks are particularly difficult in this regard as leakage may go unnoticed due to their location being obscured by cargo.
The Club draws attention to the following points:
- Investigation generally shows these incidents happen because of a disregard for the safety procedure, an incomplete risk assessment or an improper close out of the permit to work.
- All work carried out on board a vessel that poses a risk to personnel, environment, vessel or cargo should be accompanied by a permit to work issued as per the Safety Management System. Safe working procedures, along with control measures, are to be developed based on a risk assessment carried out by a competent person.
- The permit to work is issued by an authorised person who is also responsible for the close out of the permit upon successful completion and verification of the task
- It is imperative that the risk assessment which forms the basis for the safety procedure and control measures should include the entire work process required for returning the vessel to its original safe condition upon completion of the task and not just limited to the main task at hand. It is also important that the permit to work is fully verified before closing out.
- The crew should be familiar with the required manhole cover standards as stated on the ship tank arrangement plan and use only the prescribed spares.
- Control measures should also include hydrostatic pressure testing of the tank upon completion of the work. The permit to work should not to be closed until the tank has been secured and the hydrostatic pressure testing has been completed.